From U.S. Pat. No. 5,928,201 is known a device by which a dose is set by operating a pair of dose setting buttons, one increasing the set dose step by step and another decreasing the dose step by step when operated. The set dose is stored in a circuit which controls a display to show the set dose and a motor drives a mechanical dose setting device to carefully set a mechanical dose setting device to the dose shown in the display. The injection is performed manually to allow the user to inject the dose with the rate he finds appropriate.
It may be attractive to let the injection be performed electro-mechanically too as then the demand to the users finger strength can be reduced to the force needed to press down an electronic switch button. Further, the mechanical impact on the device is independent on the strength of the user so it is avoided that some users can hardly operate the device whereas others will break it.
Devices wherein the doses are electronically represented also may contain circuitry wherein historical data are stored so it is possible to create a picture of the way the user has followed his treatment, and prospective doses and time intervals can be planned on the basis of the stored data. At least it is appropriate to be able to store the size of the latest injected dose and the time passed since this injection.
In an electronic injection device of the kind described above only a minimum of operation buttons are needed, e.g., a counting up dose set button allowing a stepwise increase of the set dose, a counting down dose set button allowing a stepwise decrease of an erroneously too high set dose, and an injection button by which either the dose is manually injected or the electronic circuit is ordered to energize a motor to inject the set dose.
By injecting medicine from an ampule it is necessary to ensure that no air is left in the ampule when the injection is performed. For this purpose a so-called air-shot is performed. An air shot may be performed by setting a small dose, e.g., one international unit of the medicine to be injected, and make this small dose be pressed out from the ampule holding the device with the needle pointing vertically upward. This procedure can be repeated until it is seen that liquid is sprayed out through the needle where after the dose to be injected can be set, the needle can be inserted into the skin of the user, and an amount of medicine corresponding to the set dose can be pressed out and injected through the needle.
However, this repetitive use of the dose-setting device is not wanted. If the device is provided with a memory which stores historical data for the purpose of controlling the course of a treatment, it is necessary to register which of the doses have been air shot doses and which doses have actually been injected. This problem could be overcome by providing a special air shot button as it is known from syringes by which the injection is performed manually, but this will be on the account of one more button whereby the possibilities for erroneous operation is increased.
An objective of the invention is to provide an injection device by which repetitive air shots can be performed without adding extra operation buttons to the device and without information of the air-shots being stored as a part of the operation history of the device.
This is obtained by an electronic injection device comprising a housing containing an electronic circuit into which the size of a set dose can be read by operation of dose setting means, an injection button which can be operated to inject a set dose, an ampule from which a medicine can be pressed out through a needle mounted at the distal end of the ampule when the injection button is operated, and a display driven by the electronic circuit to show the dose set by operation of the dose setting means.
It is attractive to set the dose electronically and show the set dose on an electronic display, e.g., an LCD display, as the size of the digits displayed can be made arbitrarily large without being dependent on the distances possible mechanical dose setting parts are moved by the setting of the dose.
The device according to the invention is characterized in that the electronic circuit is designed to work in two alternative modes: an air shot mode in which it controls an automatic pre-setting of a small air shot dose to be pressed out from the ampule when the injection button is actuated, and a dose injection mode in which a dose set by operation of the dose setting means is injected by operation of the injection button, said circuit normally working in the air shot mode but shifting to work in the dose injection mode when it receives a signal indicating that the dose setting means has been operated. The circuit may return to its air shot mode when receiving a signal indicating that a set dose has been injected. This signal may either be a signal from a switch indicating that a protection cap is mounted or a signal from a switch indicating that the injection button has been pressed.
This means that when the device is taken into use but no dose has been set the electronic circuit will work in a mode making it control either a dose setting motor to set a small air shot dose which can be injected by pressing the injection button, or control a motor to press out an air shot dose when the injection button is operated.
The injection button may now be operated one or more times while the device is held with the needle pointing upward until it is seen that liquid and not air is pressed out through the needle.
To ensure that the device is held in the correct position with the needle pointing upward a position indicator may be provided which gives off a signal to the electronic circuit when the device is held in the correct position for an air shot. The signal, which can be an opening or a closing of a switch, can be made a condition that has to be fulfilled before the electric circuit energizes the motor to prepare or perform an air shot. This way waste of medicament, due to the fact that the device is held in a position in which air in the ampule cannot reach the needle, is avoided.
According to the invention the dose setting may be electro-mechanically realized by means of an electric motor which is controlled by the electronic circuit to lift up the injection button from the housing a distance corresponding to the set dose and the injection may be performed manually by pressing home the injection button. The signal that indicates that a set dose has been injected may be a switch that is actuated when the injection button is pressed. The electronic circuit will then prepare a new air shot each time a home pressing of the injection button is performed and the circuit will remain in the air shot mode.
In devices wherein the injection is performed electro-mechanically by a motor controlled by the electronic circuit, actuation of the injection button may make a motor electro-mechanically press out a dose from the ampule, the motor being controlled by the electronic circuit to press out an automatically set small air shot dose when the circuit is working in its air shot mode, and a dose set by operation of the dose setting means when the circuit is working in its dose injection mode.
At the very moment when the dose setting member is operated the working mode of the electronic circuit is changed to an injection mode in which operation of the injection button will result in the injection of a set dose either by directly pressing out a dose corresponding to the distance the injection button has been elevated over the housing by the dose setting motor controlled by the electronic circuit, or by controlling an injection motor to inject the dose set by the operation of the dose setting member, and the circuit will remain in this mode until the injection button has been pressed.
To ensure that at least one air shot is performed in advance of an injection, the circuit may be so designed that it cannot receive a signal from the dose setting means until at least one air shot dose has been administered.
According to the invention the electronic circuit may comprise a memory wherein historical information of injected doses and the time for their injection is stored. As the electronic circuit according to its two working modes can discriminate between air shots and injection of doses set by the user, these historical data can be rid of disturbing air shot data.
The electronic circuit may further be provided with a memory wherein the size of all air shots and injections are summed and subtracted from the size of the total content of a new ampule to leave the memory with an information of the size of the remaining amount of medicine in the ampule.
The set dose currently is compared with the remaining amount of medicine in the ampule to block for setting of a dose exceeding this remaining amount.